Fix typos in comments

While reading through the SANE sources I noticed some annoying typos
in the comments.  This patch is my contribution to make the SANE
sources slightly more pleasant to read.

acinclude.m4

@@ -20,7 +20,7 @@ dnl   AC_PROG_LIBTOOL
 dnl
 
 # SANE_SET_CFLAGS(is_release)
-# Set CFLAGS. Enable/disable compilation warnings if we gcc is used.
+# Set CFLAGS. Enable/disable compilation warnings if gcc is used.
 # Warnings are enabled by default when in development cycle but disabled
 # when a release is made. The argument is_release is either yes or no.
 AC_DEFUN([SANE_SET_CFLAGS],

backend/hp-accessor.c

@@ -691,7 +691,7 @@ _gamma_vector_unscale (HpAccessorVector UNUSEDARG this, SANE_Fixed fval)
 {
   unsigned short unscaled = fval / SANE_FIX(1.0);
   if (unscaled > 255) unscaled = 255;
-  unscaled = 255 - unscaled;  /* Dont know why. But this is how it works */
+  unscaled = 255 - unscaled;  /* Don't know why. But this is how it works. */
 
   return unscaled;
 }
@@ -700,7 +700,7 @@ static SANE_Fixed
 _gamma_vector_scale (HpAccessorVector UNUSEDARG this, unsigned short val)
 {
   SANE_Fixed scaled;
-  val = 255-val;     /* Dont know why. But this is how it works */
+  val = 255-val;     /* Don't know why. But this is how it works. */
   scaled = val * SANE_FIX(1.0);
 
   return scaled;

backend/hp-option.c

@@ -114,7 +114,7 @@ static SANE_Status hp_probe_parameter_support_table (enum hp_device_compat_e
 
 #define HP_EOL -9999
 
-/* Dont need requiries for commands that are probed */
+/* Don't need requiries for commands that are probed */
 #define HP_PROBE_SCL_COMMAND 1
 
 /* Scale factor for vectors (gtk seems not to like vectors/curves

backend/hp-scl.c

@@ -905,7 +905,7 @@ hp_scsi_scl(HpScsi this, HpScl scl, int val)
 
   RETURN_IF_FAIL( hp_scsi_need(this, 10) );
 
-  /* Dont try to optimize SCL-commands like using <ESC>*a1b0c5T */
+  /* Don't try to optimize SCL-commands like using <ESC>*a1b0c5T */
   /* Some scanners have problems with it (e.g. HP Photosmart Photoscanner */
   /* with window position/extent, resolution) */
   count = sprintf((char *)this->bufp, "\033*%c%d%c", group, val, param);

backend/hp5590.c

@@ -1285,7 +1285,7 @@ sane_read (SANE_Handle handle, SANE_Byte * data,
       if (ret != SANE_STATUS_GOOD)
 	return ret;
 
-      /* Dont free bulk read state, some bytes could be left
+      /* Don't free bulk read state, some bytes could be left
        * for the next images from ADF
        */
       return SANE_STATUS_EOF;

tools/check-usb-chip.c

@@ -1408,7 +1408,7 @@ check_gl646 (struct usb_device *dev)
   return "GL646";
 }
 
-/* Same as check_gl646, except that sanity check are different. */
+/* Same as check_gl646, except that sanity checks are different. */
 static char *
 check_gl646_hp (struct usb_device *dev)
 {